Cosmology: milky way size is enormous (Introduction)

by David Turell , Friday, May 31, 2019, 23:13 (2004 days ago) @ David Turell

We are way bigger than most others:

https://www.scientificamerican.com/article/the-mighty-milky-way/?redirect=1

"Yet astronomers in the know have long realized that our galaxy is exceptional. By size alone, it’s “in the top percentile of all the galaxies that exist,” says Joss Bland-Hawthorn, an astronomer at the University of Sydney who helped compile the galaxy’s vital statistics for a 2016 article in the Annual Review of Astronomy and Astrophysics. He puts the Milky Way’s mass at a hefty 1.0 trillion to 1.6 trillion times that of the sun, outweighing the vast majority of its peers by a factor of 10 to more than a million and greatly outshining them as well.

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"In 2005, the number of known Milky Way satellites began to soar after searches of large areas of the sky uncovered a new type of galaxy, what astronomers call the ultra-faint dwarfs, even smaller and dimmer than dwarf spheroidals. Adding in the ultra-faint systems boosts the number of all known Milky Way satellite galaxies to more than 50, writes Josh Simon, an astronomer at the Carnegie Observatories in Pasadena, California, in the 2019 Annual Review of Astronomy and Astrophysics. Most are ultra-faint dwarfs; all are dimmer than the Milky Way. And last year, Simon made a surprising discovery suggesting that plenty more satellite galaxies await detection.

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“'For the next 10 years or so, I think the number of [satellite] galaxies will increase pretty dramatically,” says Vasily Belokurov, an astronomer at the University of Cambridge whose team has turned up many of the new galaxies. He suspects that the Milky Way has a total of roughly 200; even the most conservative estimates put the number at 100. And that makes the Milky Way even more of a galactic standout, in the top 1 percent, says Simon: Fully 99 percent of all galaxies would be smaller, fainter and less massive—giving our galactic home an A-plus from any cosmic teacher who grades the galaxies. If the total satellite population is as high as 200, we’d be in the top 0.5 percent.

"In short, we live in a galaxy that is far bigger, brighter and more massive than most other galaxies in the universe. And in all likelihood, so do most other life forms in the universe, if such exist. That’s because the small galaxies that throng the cosmos possess so few stars; our own galaxy has many more stars than all the galaxies revolving around it put together. So, in terms of pure numbers, if every star has exactly one planet that is exactly like Earth and teeming with life, it’s likely that most living beings in the universe reside in a galaxy that’s far above average.

"So the next time you’re speeding through intergalactic space in your brand new galaxyship—mere starships are so twenty-third century—you can brag to any aliens you meet beyond the Milky Way that you hail from a gargantuan galaxy. But chances are, so can they."

Comment: our massiveness is attested to by the number of satellite galaxies. But our uniqueness is in our rarity in the universe. We are a privileged planet in a special galaxy. God at work? The article suggests life will only be in our kind of galaxy.